The present invention generally relates to a strobe apparatus with an insulated gate bipolar transistor (hereinafter referred to as I. G. B. T.) for controlling the light emitting operation of the flash discharging tube being connected in series with a flash discharging tube, and more particularly, to a strobe apparatus characterized by a voltage supplying system to the above described flash discharging tube which becomes effective when the light is repeatedly emitted at speed.
An apparatus disclosed in U.S. Pat. No. 4,839,686 is known as a strobe apparatus using such conventional I. G. B. T. as described hereinabove.
The conventional apparatus has such a circuit construction shown in FIG. 3. The conventional apparatus comprises a direct current high-tension power supply 1 which is a known DC-DC converter circuit, a main capacitor 2 to be charged by the power supply 1, a constant voltage circuit 3, which is provided together on the above described power supply 1, for feeding the constant voltage to a light emission controlling circuit 7 to be described later, a known trigger circuit 4 for triggering a flash discharging tube 5, a controlling circuit 6, which is connected with a control means 8 within a camera body, for transferring various signals, generating various output signals such as trigger signals or the like for operating the trigger circuit 4, a light emission controlling circuit 7 for controlling the on . off of the I. G. B. T. connected in series with the flash discharging tube 5, and controlling the light emission of the above described flash discharging tube 5, and a voltage doubler circuit 9 for applying the double voltage of a charging voltage of the main capacitor 2 between the main electrodes of the flash discharging tube 5.
When a switch Sw is turned on in the above described apparatus, the direct current high-tension power supply 1 is operated so as to charge like a shown polarity the main capacity 2, a voltage doubler capacitor 9a by the outputting high tension of the above described direct current high-tension power supply 1. By the on of the switch Sw, a power supply capacitor Ce for functioning as a power supply of the control circuit 6 is charged with a low-tension power supply E, and at the same time, the capacitor 3a of the constant voltage circuit 3 is also charged. The control circuit 6 starts its operation and the light emission controlling circuit 7 is put into a light emission preparing condition.
When the light emission starting signal is inputted to the controlling circuit 6 from the controlling means 8 with each of the above described capacitors being charged, the control circuit 6 operates to output a high level signal from the output terminal Oa for turning on the transistors Qa, Qb of the light emission controlling circuit 7.
When the transistors Qa, Qb are turned on, the I. G. B. T. is turned on by the charging voltage of the capacitor 3a so as to operate the trigger circuit 4. As a result, the flash discharging tube 5 consumes the charging electric charge of the main capacitor 2 so as to emit its light.
When the light emission stopping signal is inputted into a control circuit 6 from the control means 8 on the way to the above described light emission, the controlling circuit 6 operates. The controlling circuit 6 outputs a high level signal from an output terminal Ob so as to turn on the transistors Qc, Qd of the light emission controlling circuit 7. The transistors Qb, I. G. B. T. turned on so far by it are turned off so as to stop the light emission of the flash discharging tube 5.
Such an operation as described hereinabove is a fundamental operation of the conventional apparatus shown in FIG. 3.
A strobe apparatus using such a known I. G. B. T. as described hereinabove cannot have light emission over no more, unlike from the conventional apparatus which stops the light emission with the use of the commutation capacitor. The repeated high-speed light emitting operation, smaller size of the apparatus shape can be realized.
But the above described high speed repeated light emitting operation still has the following problems.
When the period of the high speed repeated light emitting operation becomes a high period of a given high period or more, for example, a period band of several tens of Hz or more, a condition where the next light emitting operation is effected before the sufficient charging operation of the voltage doubler capacitor 9a is effected in the construction as shown in FIG. 3 is considered. The flash discharging tube 5 cannot be effected as the function of the voltage doubler circuit 9 cannot be expected, with a disadvantageous point that a light emission coming off operation is caused.
Concretely, the above described voltage doubler circuit 9a is started in its charging for the first time at a time point when the cathode potential of the flash discharging tube 5 has been put at a low level. In other words, the charging operation is not effected, as clear from the illustrated circuit construction, while the above described cathode potential remains at a high level.
The above described cathode potential, when the flash discharging tube 5 once emits its light, is known to be maintained at a high electric potential during a period from the completion of the ionized condition to the return to the initial condition if the energy supply is stopped. Also, the above described voltage doubler capacitor 9a has a proper charging time constant. When the next light emitting operation has been effected at a time point when the above described time constant is not passed during the above described period or after the above described period has passed, sufficient charging operation is not effected to the above described voltage doubler capacitor 9a. As a result, the operation of the voltage doubler circuit 9 cannot be expected.
In a case of an extremely high period exceeding the above described period band, an operation for the next light emission is effected at a time in such a condition as the light emission can be effected if the light emission discharging tube 5 is not triggered. The light emission discharging tube 5 is emitted with extreme ease. It is known that the light emission coming off operation described hereinabove is not caused.
When the smaller size and the light emitting light-quantity increase are considered to be effected in the flash discharging tube, a method of increasing an internal gas pressure so as to have a higher impedance is known. Such a method is known for having raised the discharging start voltage of the above described flash discharging tube. In the high speed repeated light emitting operation, the radiation characteristics are deteriorated due to the smaller size, the heat storing characteristics are increased due to higher impedance, light emitting start voltage is raised more. Considering the above described situation, the operation of the voltage doubler circuit cannot be expected, thus rendering the light emission of the flash discharging tube disadvantageous further.